Hydraulic tilting device for tilting a vehicle cab

ABSTRACT

A hydraulic tilting device for tilting a cab mounted on the chassis of a vehicle between a driving and a tilted position comprises a reservoir for hydraulic fluid, a pump connected to the reservoir, and a double-acting hydraulic tilting cylinder. A lost-motion conduit is provided between ports opening into a push chamber and a pull chamber in the cylinder space of the tilting cylinder when the piston/piston rod assembly is in a lost-motion range defined by the ports. When under the influence of the movements of the piston/piston rod assembly within the lost-motion range, the pull connection of the tilting cylinder causes suction of hydraulic fluid out of the reservoir, forcing hydraulic fluid from the reservoir into the pull chamber, and moving hydraulic fluid from the pull chamber to the reservoir through the lost-motion conduit. Hydraulic fluid therefore circulates when the cab is carrying out spring movements.

FIELD OF THE INVENTION

The present invention relates to a hydraulic tilting device for tiltinga cab of a vehicle between a driving position and a tilted position.

BACKGROUND OF THE INVENTION

It is generally known from the prior art to connect a cab of a vehiclein a tiltable manner to the chassis of the vehicle, so that the cab canbe tilted between a driving position, in which the vehicle can bedriven, and a tilted position, in which, for example, maintenance can becarried out on the engine situated below the cab. It is furthergenerally known for such a tilting cab in the driving position to beresiliently supported on the chassis in order to provide greater comfortfor those in the cab, in particular the driver, while the vehicle isbeing driven.

For tilting such a resiliently mounted cab, it is known to use ahydraulic tilting device with a tilting cylinder disposed between thechassis and the tilting cab. In order to ensure that while the vehicleis being driven the tilting cylinder does not interfere with the springmovements of the cab relative to the chassis, tilting devices with aso-called lost-motion mode are used. These tilting devices can bedivided largely into two types, on the one hand, a mechanical type with,for example, a lost-motion arm, which is usually pivotably connectedbetween the tilting cylinder and the cab, or with a sort ofpin-and-groove connection between the tilting cylinder and the cab, and,on the other hand, a hydraulic type.

In the case of a tilting device with a hydraulic lost-motion, thetilting cylinder exhibits a lost-motion effect. A hydraulic cab tiltingdevice of this type is known, for example from GB 2 079 378.

It is proposed in this publication that when the vehicle is being drivenand the cab is carrying out spring movements, the piston/piston-rodassembly can move up and down unimpeded, since the piston is in alost-motion range that is defined by the two ports of the lost-motionconduit. In this case the pump of the tilting device is out of action inthis lost-motion mode.

In the case of this known tilting device anti-suction valves areprovided in the fluid line system in such a way that in the lost-motionmode said valves ensure that fluid cannot be sucked out of the reservoirand cannot enter the cylinder space of the tilting cylinder. The resultthat is intended to be achieved with this in the case of the knowntilting device is that the movement up and down of the piston/piston rodassembly in the lost-motion mode should lead to the displacement of acertain quantity of hydraulic fluid out of the tilting cylinder. Theobject of this is to create a vacuum in the cylinder space of thetilting cylinder, since the suction of fluid out of the reservoir isblocked. The object of the vacuum is to impede the movement up and downof the piston/piston rod assembly as little as possible in thelost-motion mode, so that the spring movement of the cab directlyconnected to the piston/piston rod assembly is not disrupted.

It appears from experiments that the tilting device proposed in GB 2 079378 does not function as expected. In particular, it appears that thefunctioning of the lost-motion mode in the manner described in GB 2 079378 cannot be guaranteed during the envisaged service life of such atilting device. It is pointed out that during that service life thepiston/piston rod assembly will move up and down many millions of timesin the lost-motion mode.

It is in fact found that the known tilting device is susceptible to twophenomena.

The first phenomenon is that, taking into account the envisaged servicelife, there is a great chance that at a certain point in time thesealing effect of the piston rod seal will be inadequate, so that airwill be able to enter the cylinder space. In this case the vacuum thatprevails during the lost-motion mode has an adverse effect on thatsealing effect.

The second phenomenon is that the valve in the lost-motion conduit isset to open at a certain hydraulic pressure and otherwise to seal offthat lost-motion conduit. Again taking into account the envisagedservice life, the functioning of this valve will also deviate from theenvisaged functioning after some time, for example owing to almostunavoidable wear. In particular, there is a considerable chance of thevalve at some point opening at a pressure that is lower than thatintended.

As a result of these phenomena, it can happen that air is sucked inalong the piston rod seal. Such air, once sucked in, remains in thehydraulic system of the tilting device. The air sucked in causes anexcessively large quantity of fluid to be forced out of the tiltingcylinder to the reservoir, by way of the lost-motion conduit and thepush chamber, with the result that the pressure in said reservoirincreases and the reservoir may overflow. The quantity of fluid forcedout is particularly great if the opening pressure of the valve in thelost-motion conduit is lower than was originally envisaged, which can bethe consequence of the almost unavoidable wear of that valve.

The air sucked in does not interfere greatly with the lost-motion effectof the tilting cylinder, but constitutes a problem in particular whenthe cab is subsequently being tilted by means of the tilting device. Itcan then, in fact, happen that the cab tips forward abruptly with anenormous bang as soon as the centre of gravity of the cab passes thepivot point relative to the chassis. The cause of that undesirable andpotentially dangerous movement of the cab is the air present in the pullchamber of the tilting cylinder.

Another risk is that so much air is sucked in that hydraulic fluid flowsout of the reservoir and a shortage of fluid arises. That shortage canbe such that the tilting of the cab cannot be carried out properly or atall. There is also a considerable chance then of the shortage ofhydraulic fluid being made up, but of the tilting device, in particularthe pull chamber, being inadequately vented. The problem mentionedearlier can occur again as a result of this.

OBJECT OF THE INVENTION

The present invention aims to provide a reliably functioning cab tiltingdevice with a hydraulic lost-motion effect.

SUMMARY OF THE INVENTION

The present invention achieves this object by providing a tiltingdevice, which is characterized in that the tilting device is designed insuch a way that during the movements up and down of the piston of thepiston/piston rod assembly within the lost-motion range hydraulic fluidis supplied from the reservoir to the pull chamber by way of the pullconnection, and in that hydraulic fluid is moved from the pull chamberto the reservoir by way of the lost-motion conduit, possibly by way ofthe push chamber, so that a circulation of hydraulic fluid occurs in itsentirety if the cab is carrying out spring movements.

The tilting device according to the invention is based on the followinginsight. The supply of hydraulic fluid occurring time and again from thereservoir to the pull chamber is caused by suction from the pull chamberand/or propulsion from the reservoir. This now desirable supply of fluidensures that the pressure in the pull chamber can constantly recover. Itis pointed out here that the reservoir, which is an airtightconstruction, acts as an accumulator, in which fluid is storedfirst—which is accompanied by an increase in pressure—and fluid is thenreleased again to the pull chamber. In order to achieve the effectdescribed above, only a slight fluid volume need be circulated in eachcase. It is even considered advantageous for the circulated volume to beas small as possible, because when large fluid volumes are circulatedthe flow resistances in the hydraulic system interfere with theenvisaged circulation effect. The correct circulation can be obtained bysynchronizing the opening pressures of the valves in the system and theresistances formed by the various throttling devices and the lines.

Advantageous embodiments of the tilting device according to theinvention will be described below with reference to the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the hydraulic diagram of an exemplary embodiment of thetilting device according to the invention,

FIG. 2 shows the hydraulic diagram of another exemplary embodiment ofthe tilting device according to the invention, and

FIG. 3 shows the hydraulic diagram of another exemplary embodiment ofthe tilting device according to the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The hydraulic tilting devices according to the invention shown in FIGS.1, 2 and 3 are intended for tilting the driver's cab of a vehicle, inparticular of a lorry. Such cabs are usually fitted on the chassis ofthe vehicle and are connected to the chassis so that they can tilt byway of pivoting means. The pivoting means are designed in such a waythat the cab can tilt between a driving position, in which the vehiclecan be driven, and a tilted position, generally forward, in which, forexample, maintenance can be carried out on the vehicle, in particular onthe engine of the vehicle, which is fully or partially situated belowthe cab.

Such vehicles are also usually provided with resilient cab supportingmeans, which support the cab in the driving position, in such a way thatin the driving position the cab can spring up and down relative to thechassis, thus increasing the comfort of the driver. The hydraulictilting device is provided for tilting the cab forward and back again.

The tilting device comprises an airtight reservoir 1 for hydraulicfluid, the inside of the reservoir being sealed off from the outsideair. A pressure-limiting valve 2 limits the pressure in the reservoir 1to a predetermined pressure value above atmospheric pressure, forexample to a pressure of 1.5 bar above the outside air pressure.

The tilting device of FIG. 1 further comprises a pump 3, which isconnected to the reservoir 1, and in this case is of the type with asingle delivery port 4 for delivering fluid under pressure, for examplea hand pump.

FIGS. 1, 2 and 3 further show a double-acting, linear hydraulic tiltingcylinder 5, for tilting the driver's cab (not shown). The cylinder 5comprises a cylinder housing 6, containing a cylinder space 7, in whicha piston/piston rod assembly can move up and down. The piston/piston rodassembly comprises a piston 8 and a piston rod 9 immovably connected toit. Around the piston B lies a sealing ring 10, while the piston rod 9projects outwards out of the cylinder housing 6 through a piston rodseal 11. The cylinder 5 is normally disposed between the cab and thechassis of the vehicle, the cylinder housing 6 generally being connectedin a swivellable manner to the chassis, and the end of the piston rod 9generally being connected in a swivellable manner to the cab.

The piston/piston rod assembly 8, 9 forms a pull chamber 12 in thecylinder space 7, which pull chamber retracts the piston/piston rodassembly when hydraulic fluid is supplied to it, and a push chamber 13,which extends the piston/piston rod assembly when hydraulic fluid issupplied to it. A corresponding pull connection 14 and push connection15 are provided for the pull chamber 12 and the push chamber 13respectively.

A first hydraulic line 16 connects to the pull connection 14, and asecond hydraulic line 17 connects to the push connection 15. The lines16, 17 are connected at the other end to a corresponding port 18, 19 ofa two-position control valve 20. Said control valve has two furtherports 21, 22, which are in communication with the delivery port 4 of thepump 3 and with the reservoir 1 respectively.

A non-return valve 23, which closes in the direction of the pump 3, isaccommodated in the connection with the delivery port 4.

In the second line 17 a hydraulically operated non-return valve 30 isaccommodated near the push connection 15, which non-return valve closesin the direction of the valve 20 and opens if sufficient hydraulicpressure is present in the control line 31 connected to the line 16.

A suction-blocking device is accommodated in the second line 17, betweenthe non-return valve 30 and the control valve 20, which suction-blockingdevice prevents unimpeded suction of fluid through the line 17. Thatdevice could be composed of two non-return valves 34, 35 positionedparallel to each other and working in opposite directions, as showndiagrammatically in the figures. However, in practice, provision can bemade for an O-ring to be fitted in a bore, and for a ball which at acertain pressure is forced through the O-ring. When the ball has thengone past the O-ring, the passage is clear. The rigidity of the O-ringin combination with the dimensions of the O-ring and the ball arelargely the determining factors for the pressure at which the ballpasses through the O-ring, in practice, for example 7 bar at roomtemperature.

In this embodiment no further valves in addition to the valves 20 and 23(integral with the pump) are present between the pull chamber 12 and thepump 3. A throttling device 36 is provided near the pull connection 14in the line 16.

A pressure-relief valve 37, placed between the first line 16 and thereservoir 1, is provided in order to prevent an excessively highpressure of the fluid in the hydraulic circuit.

The tilting device also comprises a lost-motion conduit 40 with twoports opening into the cylinder space 7, indicated by 41 and 42respectively, it being possible for the port 41 to coincide with thepush connection 15 of the cylinder 5.

The lost-motion conduit 40 is shown diagrammatically and can be designedin various ways. For instance, it is possible for the lost-motionconduit 40 to be formed by a lost-motion line lying along the outside ofthe cylinder housing 6. However, it is also conceivable for thelost-motion conduit to be provided in the cylinder housing 6. In yetanother variant the lost-motion conduit 40 is provided in a tubeextending upwards from the bottom of the cylinder housing 6 in thecylinder space.

The lost-motion conduit 40 connects the pull chamber 12 to the pushchamber 13 when the piston 8 is situated between the two ports 41, 42 ofthe conduit 40, which is the case in a position of the piston/piston rodassembly associated with the driving position of the cab. When thevehicle is being driven the pump 3 is out of action and the tiltingdevice is operating in its lost-motion mode.

A non-return valve 43 is accommodated in the lost-motion conduit 40,which non-return valve closes in the direction of the port 42, whichport 42 in the lost-motion mode of the tilting device opens into thepull chamber 12.

The hydraulic tilting device illustrated further comprises ahydraulically operated slide valve 50 of the two-way/two-position 2/2type with spring return. The valve 50 has a first valve port 52, whichis connected to the push chamber 13 of the cylinder 5, and a secondvalve port 53, which is connected to the line 17 between the valve set34, 35 and the non-return valve 30.

The valve 50 has a sliding element which is slidable in the valvehousing and is hydraulically adjustable to the open position under theinfluence of hydraulic pressure by way of the control line 54 and thecontrol line 55. The control line 54 is directly connected to the pushchamber 13, and the control line 55 is connected to the line 17 betweenthe valve set 34, 35 and the non-return valve 30.

By way of control line 56, which is in direct communication with theport 42, a hydraulic pressure can be exerted upon the sliding element,forcing the sliding element to the closed position.

If the process is stopped during forward tilting of the cab, and the cabis going to fall back to the driving position again under its ownweight, then the non-return valve 30 closes. If the piston 8 is situatedabove the port 42 at the time of stopping, the valve 50 also remainsclosed, because the hydraulic pressure in the push chamber 12 then actsupon the sliding element by way of the control line 56. In this way thepiston/piston rod assembly is held reliably in place, which is of greatimportance for the safety of the persons who at the time are moving toor are already in a position below the cab.

When the cab has to be tilted out of the tilted position to the drivingposition, i.e. the piston rod 9 has to be retracted, fluid is suppliedby way of delivery port 4 to the pull chamber 12. The pressure in thefirst line 16 causes the non-return valve 30 to open, and fluid can flowout of the push chamber 13. If the tilting back is interrupted in aposition in which the piston 8 is situated above the port 42, the valve50 is held in the closed position. The valve 30 also closes, so that thecab then remains at a standstill. If during the tilting back of the cabto the driving position the piston 8 has already passed the port 42,then the pressure falls away in the part of the lost-motion conduit 40between the valve 43 and port 42. This causes the pressure in the line56 also to fall away, and the valve 50 is opened through the pressureprevailing in line 54. The result is that the fluid can flow out of thepush chamber 13 to the reservoir 1, and the cab can tip back furtherunimpeded to the driving position, an orifice also being provided inorder to limit the speed of movement of the cab. This “free-fallmovement” of the cab is desirable in many cases, in order to make thecab lock with one or more cab locking devices, which are fitted on thechassis and secure the cab in the driving position. A relatively rapidtilting movement of the cab is often advantageous for producing theengagement between the cab and such locking devices.

When the cab is in the driving position and the tilting device isbrought into the lost-motion mode, which here simply means that the pump3 is switched off and the valve 20 is in its illustrated position, thenthe device shown in FIG. 1 works as follows.

When the cab makes such a spring movement that the piston rod 9 is drawnout of the cylinder housing 6, fluid flows out of the pull chamber 12 byway of the port 42, and then passes by way of the line 40, through theopening non-return valve 43, into the push chamber 13. The valve 50remains closed here.

When the cab moves in such a way that the piston rod 9 is forced intothe cylinder housing 6, fluid flows out of the push chamber 13 by way ofthe open valve 50 to the reservoir 1. In this situation the valve 50opens because a hydraulic pressure is exerted upon a control pressureopening surface of the sliding element by way of the control pressureline 54. At the same time no hydraulic pressure is acting upon theclosing surface of the sliding element, so that only the (light) spring58 is counteracting the opening of the valve 50.

When the cab moves in such a way that the piston rod 9 is forced intothe cylinder housing 6, hydraulic fluid is also sucked out of thereservoir 1 by way of the line 16. A (slight) vacuum in fact occurs inthe pull chamber 12, which vacuum, possibly in conjunction with thepressure above atmospheric pressure in the reservoir 1, leads to a flowof fluid out of the reservoir, along the weak non-return valve 23 to thepull connection. In this way the pull chamber 12 remains filled withhydraulic fluid. The opening pressure of the valve 23 is preferably low,preferably less than 0.5 bar, for example approximately 0.2 bar. Inorder to prevent too great a flow of hydraulic fluid, the throttlingdevice 36 is provided, which throttling device can be composed of twobores of small diameter, for example 0.5 millimeter, placed one behindthe other.

In its entirety, what is now achieved is that while the vehicle is beingdriven, during which time the cab constantly springs up and down,hydraulic fluid is circulated through the hydraulic circuit of thetilting device. The direction of flow here is from the reservoir 1 tothe pull chamber, by way of the lost-motion conduit 40, to the pushchamber 13, and from the push chamber 13, by way of the valve 50, backto the reservoir 1.

The first advantage of the circulation of hydraulic fluid is that fluidis supplied constantly to the pull chamber 12, so that even if air wereto leak along the piston rod seal 11 into the pull chamber 12, it wouldbe a minimum quantity here. The pressure in the pull chamber 12 can thusconstantly adjust to the value set by the valve 43.

The pressure in the pull chamber 12 is now determined by the openingpressure of the valve 43 in the lost-motion conduit 40 and the pressurein the push chamber 13. In practice, a maximum pressure of, for example,2.5 bar above atmospheric pressure could be achieved in the pull chamber12 in the lost-motion mode. If that pressure prevails in the pullchamber 12, in the embodiment illustrated a pressure of approximately 1bar below atmospheric pressure prevails in the push chamber. The maximumpressure in the push chamber 13 is then between 0.5 and 2 bar aboveatmospheric pressure, which last value prevails at a minimum pressure inthe pull chamber 12.

FIG. 2 shows a tilting device which corresponds largely to the tiltingdevice according to FIG. 1. The difference is in particular that in thiscase a preferably electrically driven pump 60 of the reversible type isused, having two ports 61, 62, which serve as delivery port or suctionport depending on the pumping direction. Components of the tiltingdevice in FIG. 2 which correspond to components shown in FIG. 1 areprovided with the same reference numerals. A suction exchange valve 64and two pressure-relief valves 65, 66 can also be seen in FIG. 2. In thelight of the description with reference to FIG. 1, it will be clear tothe person skilled in the art that here again a circulation of hydraulicfluid occurs during the lost-motion mode.

FIG. 3 shows a variant of the tilting device according to FIG. 1.Corresponding parts are provided with the same reference numerals.

In the case of the tilting device according to FIG. 3 an additionalvalve 67 is provided compared with the tilting device according to FIG.1. Said valve 67 is fitted in the common part of the lost-motion conduit40 and the second line 17, which at the common port 41, 15 connects tothe push chamber 13 of the cylinder 5. The lost-motion conduit 40 isthus in communication with the second line 17.

The valve 67 is designed to connect the push chamber 13 to, or incertain conditions to shut it off from, the lost-motion conduit 40 andthe second line 17.

The valve 67 is a hydraulically controlled slide valve of thetwo-way/two-position 2/2 type with spring reset to the closed positionby means of spring 68.

The valve 67 has a sliding element which is hydraulically adjustableunder the influence of hydraulic pressure by way of the control lines69, 70, 71.

When hydraulic fluid is supplied under pressure by means of the pump 3to the second line 17, the valve 67 opens under the influence of thehydraulic pressure by way of control line 71. If the piston 8 is withinthe lost-motion range, the valve 67 will open as soon as the force byway of the pressure along control line 71 is equal to the force of thespring 68. If the piston 8 is outside the lost-motion range, the valve67 opens if the pressure at control line 71 is equal to the pressure inthe push chamber 13 and the force of the spring 68.

When hydraulic fluid is supplied under pressure by means of the pump 3to the first line 16, so long as the port 42 is still connected to thepush chamber 13 the valve 67 will remain closed under the influence ofthe pressure by way of the control line 69 and 70. The fluid then flowsthrough the lost-motion conduit 40 and by way of the non-return valve 30out of the push chamber 13. If the piston 8 goes within the lost-motionrange, the pressure in control line 69 falls away and the valve 67 isopened by the pressure in control line 70.

During the inward movement of the piston 8 in the lost-motion mode ofthe tilting device a build-up of pressure in the push chamber 13 causesthe valve 67 to be opened by way of the control line 70.

During an outward movement of the piston 8 in the lost-motion mode abuild-up of pressure occurs in the control lines 69 and 71. Owing to thefact that the surfaces upon which these control pressures act aredifferent, the valve 67 remains closed. The circulation flow of fluidout of the pull chamber 12 occurs through the lost-motion conduit 40directly by way of the valve 30 (which opens under the influence ofcontrol pressure through line 31) to the reservoir 1. This flowtherefore does not pass through the push chamber 13 here.

As a result of the valve 67, the anti-suction valves 34, 35 in FIG. 1are no longer necessary.

It will be clear to the person skilled in the art that the inventiveidea described can also be achieved in the case of hydraulic tiltingdevices with a hydraulic diagram that differs in one or more points. Forinstance, it is conceivable for the valves 30 and 43 to be integral inthe slide valve 50.

The inventive idea can also be implemented in the tilting devicedescribed in DE 197 30 499 with reference to FIG. 1 of that Germanpublication. In this case it is sufficient in the case of that knowntilting device to dispense with the anti-suction valves 29, 30 (assembly132) in the line 16 to the pull chamber of the tilting cylinder and tomake the reservoir an airtight reservoir with excess-pressure valve, asexplained here earlier with reference to FIG. 1 of this presentinvention. No anti-suction valves need be present in the line 20 of theknown tilting device either.

1. A hydraulic tilting device for tilting a cab of a vehicle between adriving position and a tilted position, which cab in the drivingposition is resiliently supported on a chassis of the vehicle, whichtilting device comprises: a reservoir for hydraulic fluid, a pumpconnected to the reservoir and having a delivery port for deliveringhydraulic fluid under pressure; a double-acting, hydraulic tiltingcylinder, for tilting the cab, comprising a cylinder housing, containinga cylinder space, and comprising a piston/piston rod assembly includinga piston and a piston rod, which piston/piston rod assembly is moveableback and forth in said cylinder space, the piston rod of which assemblyprojects outwards out of the cylinder housing through a correspondingpiston rod seal, which piston/piston rod assembly forms a pull chamberin the cylinder space, so that the piston/piston rod assembly isretracted when hydraulic fluid is supplied to said pull chamber, and apush chamber, so that the piston/piston rod assembly is extended whenhydraulic fluid is supplied to said push chamber, a corresponding pullconnection and push connection being provided for the pull chamber andthe push chamber, in which the tilting cylinder is further provided witha lost-motion conduit, extending between ports which open into thecylinder space of the tilting cylinder, which ports are in communicationwith the push chamber and the pull chamber respectively if the piston ofthe piston/piston rod assembly is in a lost-motion range defined by theports, the piston/piston rod assembly being able to move within saidlost-motion range if the cab is carrying out spring movements in itsdriving position, a valve, which is disposed in the lost-motion conduitand can shut off the lost-motion conduit, a line system, such that thepull connection and the push connection are connectable to the deliveryport of the pump or the reservoir, wherein the tilting device isdesigned such that during movements of the piston of the piston/pistonrod assembly within the lost-motion range hydraulic fluid is suppliedfrom the reservoir to the pull chamber by way of the pull connection,and wherein hydraulic fluid is moved from the pull chamber to thereservoir by way of the lost-motion conduit, so that in general acirculation of hydraulic fluid occurs if the cab is carrying out springmovements.
 2. A tilting device according to claim 1, wherein said valveis a valve which closes in the direction of the pull chamber and opensat a predetermined opening pressure in the pull chamber.
 3. A tiltingdevice according to claim 1, in which the tilting device is designedsuch that during movements of the piston of the piston/piston rodassembly within the lost-motion range hydraulic fluid is supplied fromthe reservoir to the pull chamber by way of the pull connection, and inwhich hydraulic fluid is moved from the pull chamber to the push chamberby way of the lost-motion conduit, and in which hydraulic fluid isdischarged from the push chamber to the reservoir, so that a circulationof hydraulic fluid occurs in its entirety if the cab is carrying outspring movements.
 4. A tilting device according to claim 1, in which thereservoir is airtight with a pressure-relief valve, in such a way thatthe maximum reservoir pressure in the reservoir is limited to a pressureabove atmospheric pressure, so that the reservoir pressure contributesto the supply of hydraulic fluid to the pull chamber.
 5. A tiltingdevice according to claim 4, in which the maximum reservoir pressure is1.5 bar above the outside air pressure.
 6. A tilting device according toclaim 1, in which in the line system between the reservoir and the pullconnection, in particular between the delivery port of the pump and thepull connection, if suction from the reservoir is possible by way of thepump, a non-return valve closing in the direction of the reservoir isaccommodated, which non-return valve opens at an opening pressure, whichopening pressure is advantageously less than 0.5 bar.
 7. A tiltingdevice according to claim 1, in which in the line system between thereservoir and the pull connection a throttling device is accommodated.8. A tilting device according to claim 1, in which in the line systembetween the reservoir and the pull connection a throttling device isaccommodated having one or more bores disposed one after the other andhaving a diameter of approximately 0.5 millimeter.
 9. A tilting deviceaccording to claim 1, in which a hydraulically operated slide valve isprovided, which slide valve has a first valve port, which is connectedto the push chamber, a second valve port, which at least in thelost-motion mode is connected to the reservoir, and a sliding element,which is slidable between a closing position, in which the first andsecond valve ports are shut off from each other, and an openingposition, in which the first and second valve ports are in communicationwith each other, the slide valve being provided with a spring meanswhich loads the sliding element in the direction of its closingposition, and in which an opening control surface is associated with thesliding element, which opening control surface by way of a control lineis in communication with the push chamber, so that a hydraulic pressurein the push chamber acts upon the opening control surface in order toforce the sliding element to the opening position, and a closing controlsurface being present, which by way of a control line is connected tothe cylinder space, so that a hydraulic pressure in the push chamberacts upon the closing control surface in order to force the slidingelement to the closing position.
 10. A vehicle, comprising a tiltingcab, a chassis and pivoting means, which connect the cab to the chassis,in which the cab is tiltable through an angle relative to the chassisabout a pivot pin defined by the pivoting means, between a drivingposition and a tilted position, and in which the cab is resilientlysupported on the chassis, and a hydraulic tilting device according toclaim 1 is provided, in order to tip the cab, the tilting cylinder beingfitted directly between the chassis and the cab.
 11. A tilting deviceaccording to claim 6, wherein said opening pressure is approximately 0.2bar.